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2874c5fd | 1 | // SPDX-License-Identifier: GPL-2.0-or-later |
6ae7440e JC |
2 | /* |
3 | * Copyright (C) 2006 Jim Cromie | |
4 | * | |
5 | * This is a clocksource driver for the Geode SCx200's 1 or 27 MHz | |
6 | * high-resolution timer. The Geode SC-1100 (at least) has a buggy | |
7 | * time stamp counter (TSC), which loses time unless 'idle=poll' is | |
8 | * given as a boot-arg. In its absence, the Generic Timekeeping code | |
9 | * will detect and de-rate the bad TSC, allowing this timer to take | |
10 | * over timekeeping duties. | |
11 | * | |
12 | * Based on work by John Stultz, and Ted Phelps (in a 2.6.12-rc6 patch) | |
6ae7440e JC |
13 | */ |
14 | ||
15 | #include <linux/clocksource.h> | |
16 | #include <linux/init.h> | |
17 | #include <linux/module.h> | |
18 | #include <linux/ioport.h> | |
19 | #include <linux/scx200.h> | |
20 | ||
21 | #define NAME "scx200_hrt" | |
22 | ||
23 | static int mhz27; | |
24 | module_param(mhz27, int, 0); /* load time only */ | |
25 | MODULE_PARM_DESC(mhz27, "count at 27.0 MHz (default is 1.0 MHz)"); | |
26 | ||
27 | static int ppm; | |
28 | module_param(ppm, int, 0); /* load time only */ | |
29 | MODULE_PARM_DESC(ppm, "+-adjust to actual XO freq (ppm)"); | |
30 | ||
31 | /* HiRes Timer configuration register address */ | |
32 | #define SCx200_TMCNFG_OFFSET (SCx200_TIMER_OFFSET + 5) | |
33 | ||
34 | /* and config settings */ | |
35 | #define HR_TMEN (1 << 0) /* timer interrupt enable */ | |
36 | #define HR_TMCLKSEL (1 << 1) /* 1|0 counts at 27|1 MHz */ | |
37 | #define HR_TM27MPD (1 << 2) /* 1 turns off input clock (power-down) */ | |
38 | ||
39 | /* The base timer frequency, * 27 if selected */ | |
40 | #define HRT_FREQ 1000000 | |
41 | ||
a5a1d1c2 | 42 | static u64 read_hrt(struct clocksource *cs) |
6ae7440e JC |
43 | { |
44 | /* Read the timer value */ | |
a5a1d1c2 | 45 | return (u64) inl(scx200_cb_base + SCx200_TIMER_OFFSET); |
6ae7440e JC |
46 | } |
47 | ||
6ae7440e JC |
48 | static struct clocksource cs_hrt = { |
49 | .name = "scx200_hrt", | |
50 | .rating = 250, | |
51 | .read = read_hrt, | |
52 | .mask = CLOCKSOURCE_MASK(32), | |
73b08d2a | 53 | .flags = CLOCK_SOURCE_IS_CONTINUOUS, |
6ae7440e JC |
54 | /* mult, shift are set based on mhz27 flag */ |
55 | }; | |
56 | ||
57 | static int __init init_hrt_clocksource(void) | |
58 | { | |
12d6d412 | 59 | u32 freq; |
856fe98f | 60 | /* Make sure scx200 has initialized the configuration block */ |
6ae7440e JC |
61 | if (!scx200_cb_present()) |
62 | return -ENODEV; | |
63 | ||
64 | /* Reserve the timer's ISA io-region for ourselves */ | |
65 | if (!request_region(scx200_cb_base + SCx200_TIMER_OFFSET, | |
66 | SCx200_TIMER_SIZE, | |
67 | "NatSemi SCx200 High-Resolution Timer")) { | |
d976f762 | 68 | pr_warn("unable to lock timer region\n"); |
6ae7440e JC |
69 | return -ENODEV; |
70 | } | |
71 | ||
72 | /* write timer config */ | |
856fe98f | 73 | outb(HR_TMEN | (mhz27 ? HR_TMCLKSEL : 0), |
6ae7440e JC |
74 | scx200_cb_base + SCx200_TMCNFG_OFFSET); |
75 | ||
12d6d412 JS |
76 | freq = (HRT_FREQ + ppm); |
77 | if (mhz27) | |
78 | freq *= 27; | |
79 | ||
10ea9d6f | 80 | pr_info("enabling scx200 high-res timer (%s MHz +%d ppm)\n", mhz27 ? "27":"1", ppm); |
6ae7440e | 81 | |
12d6d412 | 82 | return clocksource_register_hz(&cs_hrt, freq); |
6ae7440e JC |
83 | } |
84 | ||
85 | module_init(init_hrt_clocksource); | |
86 | ||
87 | MODULE_AUTHOR("Jim Cromie <jim.cromie@gmail.com>"); | |
88 | MODULE_DESCRIPTION("clocksource on SCx200 HiRes Timer"); | |
89 | MODULE_LICENSE("GPL"); |